This project is concerned with problems central to peripheral T cell tolerance. We believe that critical molecular intermediates that govern T cell receptor specific anergy remain to be clarified. A number of signaling pathways appear to be affected during tolerance, inducing, and several biochemical alterations contribute to desensitization of receptor mediated responses in the anergic cells. While some the principles that govern dampening of T cell receptor associated signaling are generally understood, most detailed information is either not available or is inconsistent. In some similar in vitro tolerance systems apparent inconsistencies in biochemical alterations need to be explained. Differences also exist in the purported molecular processes that characterize the anergy analyzed in vitro using clones or in vivo using whole populations tolerized by soluble antigens or superantigens. In general, changes in receptor assemblies as complex as the T cell antigen receptor complex have been difficult to analyze. T cell clones which have been extensively selected for their ability to grow in certain media have often been used, and differences in functional responses may be influenced by the absence of suitable markers that permit purification of anergic cells that could then by analyzed using sensitive biochemical or molecular approaches. We have identified a T cell marker, 6C10, that can be used to isolate anergic T cells from the peripheral pool of lymphocytes in a transgenic mouse model that we have developed. We are now in a unique position to characterize the biochemistry and function of in vivo tolerant T cells. We have significant skills in molecular, protein and structural analyses and feel we can determine both the differences and similarities in the T cell receptor complexes and certain signaling components isolated from tolerant versus normal CD4+ T cells. All of the reagents have been accumulated, and a transgenic strain has been generated that should allow us to analyze the function of truly tolerant T cells in vivo in a simple model of transferable tolerance.